Workpiece shape control with a rolling mill



May 3, 1966 A. F. KENYON ETAL 3,248,916

WORKPIECE SHAPE CONTROL WITH Av ROLLING MILL Filed April 29, 1963 5 Sheets-Sheet l 42 CARO-READER V scREwOOwN POsnTnON CONTROL l @F COMPUTER 3o 33x 3R* 37 MEM an 35\ www TRTORRESG l O TmcKNEss wTOTR GAUGE GAUGE GAUGE GAUGE g 32 i2 ls l 3G\ 1 4J 3e\ g ,AO TEMPERATURE TEMPERATURE MANUAL GAUGE le l GAUGE INPUT l l f 22 M|LL MOTOR 4 Fig.|. sPEEO CONTROL m OONVENTIONAL 4 1 MILL MOTOR APPARATUS 5,04 M C! 2D F\ 54 mcH'BAcKUP ROLL O 0. z 59 lNcH BACKUP ROLL o @3 l j :1 ROLL BENOl-RG E m ,2' go 5 N M Flag. U.. A v I e w m PRAME,SOREW,NUT $5 ROLL ELATTENTNGANO v w OOTTOM SUPPORT ,NVENTORS j Alonzo E Kenyon ond I l l l I I I J Andrew W. Smih,Jr.

l l l O 2O AO GO OO :OO |20 PRODUCT WlDTH- INCHES .'TT'NEY woRKPIEcE SHAPE CONTROL WITH A ROLLING MILL Filed April 29, 1965 May 3, 1966 A. F. KENYoN r-:TAL

5 Sheets-Sheet 2 lill-IU S Alla! May 3, 1966 A. F. KENYON ETAL 3,248,916

WORKPIECE SHAPE CONTROL WITH A ROLLING MILL 5 Sheets-Sheet 3 Filed April 29, 1963 6 L w @L g H e R ML W WE M C.. Ou... 2 UT .l RM 7 E 4 F KVM 6 1% SF Am m0 an C@ i WT N E I C O 4 lO 2 w m 1 2 1;/ W F D .l O .I 4 3 2 mOOn. OmmO wDZDO 2031-22 S N E am COR NRC May 3, 1966 MILLIONS OF POUNDS A. F. KENYON ETAL 3,248,916

WORKPIECE SHAPE CONTROL WITH A ROLLING MILL Filed Apri129, 1965 5 sheets-sheet 4 bELlvr-:RY GAUGE woRKPIECE SHAPE CONTROL WITH A RoLLlNG MILL Filed April 29, 1963 May 3, 1966 A. F. KENYoN ETAL.

5 Sheets-Sheet 5 HoT H NARROW METAL DRAFT COLD WIDE METAL MOTOR TORQUE ROLL SEPARATING FORCE T RIGHT f scREwoowN LEFT SCREWDOWN CENTER THICKNESS GAUGE SHAPE CONTROL APPARATUS LEFT THICKNESS GAUGE RIGHT THICKNESS GAUGE TIMER Fig. IO.

l of the drive motor torque at base speed.

United States Patent C) 3,248,916 WRKPIECE SHAPE CONTRUL WITH RLLING MllLL Alonzo le". Kenyon, Pittsburgh, and Andrew W. Smith,

Sir., Mount Lebanon Borough, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Apr. 29, 1963, Ser. No. 275,263 tCiaims. (Cl. 72-12) The present invention relates in general to the passing of a metal workpiece through a metal rolling mill, and more particularly to the operation of a metal rolling mill such that the delivery shape of the workpiece is controlled as desired to cause the workpiece to lie at on the delivery table.

In the operation of a rolling mill, the drafting performed on the workpiece during each pass of a given section of a workpiece between a pair of work rolls is constrained by at least four limits. One of these limits is the roll separating force between the work rolls. For any .given rolling mill there will be a maximum safe value of roll separating force, and for mills that roll a particularly thin workpiece product the roll force mustbe suicient to produce a dat plate with a given amount of roll crown. The roll force on the latter passes must be suiiicient to overcome the crown of the roll. To maintain the delivery workpiece shape along its longitudinal dimension and to equalize the mechanical loading on the mill, the roll separating force should be controlled throughout a given rolling schedule but particularly on the latter passes. Another limit is the drive motor torque. The workpiece drafting should be made within the limits rating force is maintained at a substantially constant value, the drive motor torque will diminish on the latter passes when the draft or arc of contact relative to the workpiece is less. Another limit is the maximum per unit draft or percentage draft. This limit will prevent edge cracking or other faults as a result of excessive working of the workpiece material. The fourth limit is maximum inches draft and is determined by the maximum practical bite angle which depends on the roll diameter, the roll surface, and the material being rolled.

A central rolling mill operation control device, such as a digital computer having a memory register, can 'be utilized to produce the desired shape by controlling workpiece drafting with roll force, motor torque, inches draft and percent draft as limits to the operation. The control device is initially given as input information the workpiece thickness, the workpiece width, the workpiece temperature, the material composition and the workpiece length. The control device can be programmed to pass the workpiece a given number of times through a reversing single stand mill or through the known number of stands of a tandem-mill, such that a desired workpiece thickness is scheduled to be delivered from each such pass or stand.

It is an object of the present invention to provide an improved operation of a rolling mill, such that the delivered workpiece is better shaped to be more stable in position in passing through the rolling mill and to lie flat on the work tables following the mill, and the workpiece is a predetermined amount thicker along the middle of the workpiece as compared to the thickness along the edges of the workpiece.

It is a different object to provide an improved operation of a metal rolling mill to deliver a workpiece having a predetermined percentage heaviness or thicker dimension in the middle along its whole longitudinal length, which percentage is better preserved and maintained on the nal passes when the workpiece is thinner.

If the roll sepa- It is an additional object to provide an improved operation of a metal rolling mill such that a pattern control of workpiece shape is established in accordance with the predetermined roll separation force and a Vernier or overriding control of workpiece shape is established in accordance with any undesired variation of the workpiece shape as monitored by suitable sensing devices.

It is another object of the invention to-provide improved quality and quantity of rolled products in terms of workpiece shape and better performance of the rolling mill, by more consistent duplication of the desired operational limits of roll force, motor torque availability, maximum bite angle of metal in the rolls and the maximum percentage draft that is allowed.

In accordance with the present invention, the shape or cross-sectional contour of the rolled workpiece is controlled by selecting the roll separating force to overcome the predetermined and ground crown of the rolls plus enough additional force to deliver the workpiece thicker lengthwise along the middle than along the edges as desired. For the thinner workpiece dimensions in this regard, this roll force is calculated to provide a substantially constant `workpiece percentage crown delivered from the last few passes or stands of the rolling mill.

These and other objects and advantages of the present invention will ,become apparent in view of the following description taken in conjunction with the drawings wherein:

FIGURE l is adiagrammatic showing of one form of control apparatus suitable for operation with a rolling mill in accordance with the teachings of the present invention; l FIG. 2 is a diagrammatic showing of another form of control apparatus suitable for operation witha rolling mill in accordance with the teachings of the present invention; I

FIG. 3 illustrates the crown in a pair of typical work rolls relative to the accompanying backup rolls;

FIG. 4 is a curve to illustrate the roll bending in terms of product width and mill stretch;

FIG. 5 is a showing of work rolls undergoing a considerable roll separating force to illustrate how the width of the workpiece effects the bending of the work roll and the backup rolls;

FIG. 6 is a curve to illustrate the relationship between the roll separating force and the workpiece width to produce a workpiece of substantially uniform thickness;

FIG. 7 is a curve of workpiece thickness plotted in ter-ms of the passes through a rolling mill to illustrate the scheduling of a predetermined number of passes to accomplish a desired workpiece thickness reduction;

FIG, 8 is a curve of roll separation force in terms of workpiece delivery thickness to illustrate the drafting constraint limits to control the operation of a rolling mill in accordance with the present invention;

FIG. 9 illustrates the effective constraint limits on l the drafting operation of a rolling mill; and

FIG. l0 illustrates the provision of the necessary workpiece thickness sensing devices to monitor the desired workpiece shape delivered from a rolling mill.

In FIGURE 1 there is shown a rolling mill 10 including work rolls 12 and 14 operative with backup ro1ls16 and 18. A mill motor 2t) is operative to drive the work roll 14 and is controlled in its operation by a mill motor speed control 22. A computer 24 is operative to control the mill motor 20 through the mill motor speed control 22, and in turn to receive as a feedback signal from the mill motor speed control 22 signals in accordance with the operation of the mill motor 20. A conventional mill motor apparatus 26 is operative with each arrests of the mill motor speed controls 22 and the screwdown position control 28, as is conventional in the well known operation of a rolling mill. The screwdown motor 30 is controlled and positioned to vary the roll separation force between the work rolls 12 and 14 and thereby to determine the delivery thickness of the workpiece strip 32 passing through the rolling mill 10. A thickness gauge 34 and a width gauge 35 are operative with the workpiece strip delivered from the rolling mill 10. A thickness gauge 31 and a width gauge 33 are operative at the entry side of the rolling mill 10. For a reversing mill it should be understood that the workpiece strip 32 would pass in a first direction through the rolling mill and then be reversed to pass through in the opposite direction for a desired and predetermined-number of passes through the rolling mill 10. Similarly a temperature gauge 36 is operative with the entry side of the rolling mill 10 and the temperature gauge 38 is operative with the delivery side of the rolling mill 10 for the first pass. All of the provided gauges are connected to supply suitable indication signals to the computer 24. A card reader 42 is operative with the computer 24 as is a manual input 40 for supplying predetermined information such as the initial workpiece temperature, the desired delivery thickness from each pass, the material composition and the like information.

In FIG. 2 there is provided a diagrammatic showing of one form of control apparatus operative with a tandem rolling mill in accordance with t-he teachings of the present invention. The tandem mill includes a rst stand 50, a second stand 52, and a stand S4, which might be the sixth stand for a six stand tandem mill. A screwdown position control is provided for each stand of the mill, as is a workpiece thickness gauge and a w-orkpiece temperature gauge at the delivery side of the rst and second stands 50 and 52. An X-ray gauge S6 is provided at the delivery side of the last stand 54 for providing an accurate measurement of the nal delivery workpiece thickness. The thickness gauge and temperature gauge 58 and 60 operative with the first stand 50 provides thickness and temperature signals averaged for each predetermined increment of the workpiece strip 62 passing through the first stand 50. A speed sensing device 64 is operative to measure the delivery speed of the workpiece strip 62 increments leaving the first stand 50, speed signals are supplied to a memory and shift register 66 operative with an interstand computer 68 for sequentially storing the incremental thickness and ternperature signals in synchronism with the movement of the workpiecestrip increments such that `this information is 'supplied as needed to the screwdown position control 70 for the stand 52 in synchronism with the passage of the corresponding workpiece increments through the second stand 52. A central computer '/"2 is operative with the interstand computer 68 for coordinating the control of all the stands in accordance with the desired workpiece strip delivery thickness from the respective stands. Similarly the thickness gauge 74 and the temperature gauge '76 are operative at the delivery side of the secondstand 52 with an interstand computer 78 operative with increment signals supplied to a memory and shif-t register 80 and responsive to the speed of the workpiece strip leaving the stand 52 as sensed by a speed sensing device 82 for synchronizing the incremental control information with the movement of the respective increments rbetween the second stand 52 and the next succeeding stand in the rolling mill. As the workpiece strip leaves the last stand 54, the X-ray gauge 56 provides an overriding pattern control signal for determining the operation of all the stands to provide a desired actual delivery thickness for the workpiece strip leaving the last stand 54.

In FIG. 3 there is shown work rolls 12 and 14 and backup rolls 16 and 18 which could be for the rolling V14 become substantially parallel.

d mill rst stand 10 shown in FIG. 1. It should be noted from FIGURE 3 that the work rolls 12 and 14 are provided with a predetermined crown or contour shape such that they are thicker vin their center portion than at their edge portions. This is intentional in that as the backup rolls 16 and 1S are moved together by the screwdown motor 30 shown in FIGURE 1 there is a tendency for the work rolls and the backup rolls to bend such that the cont-acting surfaces of the work rolls 12 and This partially compensates for the roll bending.

In FIG. 4 there is provided a curve to illustrate the total mill stretch for 11,000,000 pounds separation force as a function of product width from 25 inches to 130 inches wide and for 54 inch and 59 inch backup rolls respectively. This is shown as a typical illustration. The information shown in FIG. 4 can be stored in the computer 24 shown in FIGURE 1 in the form of equations such that product width and the roll diameter can be used to derive the mill spring constant of t-he rolling mill stand for controlling the operation as will be subsequently explained.

Actual test data was taken for a typical rolling mill stand to determine the total mill stand stretch. Approximately one-half the total mill stand stretch was noted in the work roll and backup roll bending and the other onehalf in the nut-screw-frame roll flattening and bottom support deflection. At a roll separating force for the particular mill in the order of 11,000,000 pounds, the total deection is in the order of 1/3 inch. For a wide plate which was relatively cold and that required the development of the full 11,000,000 pounds during the last pass, for example, thisy means it would'be necessary that the rolls be brought together and in touching contact before the workpiece strip entered the last stand of the mill in order to produce a delivery thickness of 1/3 of an inch.

FIG. 5 illustrates the bending exaggerated for clarity of the work rolls and backup rolls to be a function of product width and the roll diameters. If the workpiece passed through the rolling has a relatively narrow width .at the top and a relatively wide width at the bottom, even though the total roll separating force as seen by the top set of rolls and the bottom set of rolls would be equal, the top rolls would have the larger deflections since the -load is concentrated near the center of the rolls. The strength of the individual rolls is also affected by the roll diameter, particularly the backup roll diameter.

It is a common practice at the present time to grind the work rolls to have some crown as shown in FIG. 3 such that the diameter of the work roll at the center is greater than -the diameter of the work roll at the ends, and this is used to at least partially compensate for the roll bending such as illustrated in FIG. 5.

FIG. 6 illustrates the distribution of crown across the face of a typical mill where the center of the work roll diameter is 0.01 inch greater than the diameter at the edge of the work roll. The upper part of FIG. 6 illustrates the calculated total roll separating force required to produce a workpiece plate of substantially uniform thickness for various widths, using the 0.01 inch crown. The upper -line shows the force required when using a 72 inch 4backup roll and a lower curve illustrates the force required when using a 64 inch backup roll. As the width of the workpiece plate or strip decreases, the force required t0 produce a plate of uniform thickness also decreases.

The lower curve of FIG. 6 shows that the difference in crown between the middle of the workpiece plate or strip and the edge of the workpiece when rolling a workpiece inches wide, with 50 inches from the center line of the mill to the edge of the plate, is 0.006 inch per roll. The curve for 64 inch backup rolls shows that with this workpiece width a force of 1.5 million pounds would be required and a roll separating force of 2.7 million pounds would be required for 72 inch backup rolls to produce a substantially uniform thickness workpiece.

In actual practice it is usual to operate the mill with roll separating vforces higher than those shown in FIG. 6 to produce a workpiece shape which is thicker in the middle than along the edges. This results in a more stable rolling operation with less tendency for the workpiece to move to one side of a rolling mill stand or the other side of the rolling Imill stand as it passes through. Once the desired percentage of roll crown is determined using the final desired workpiece thickness, this same percentage crown should be used on all of the last few thin passes so that the elongation down the middle of the workpiece plate or strip would be the same as that along the edge lof the workpiece. If this is done the workpiece will lie flat on the rollaout tables even though it is slightly thicker in the middle than at the edges. This requirement is not necessary for the earlier passes when the piece is thicker because there is enough side flow of material in the bite of the roll and the workpiece has enough mechanical strength to cause it to lie flat even though there is some difference in the apparent elongation of the edges compared to the center.

The following table of information illustrates the actual passes that could be performed in accordance with the teachings of the present invention with a typical plate reversing mill.

Roll Plate Crown Pass Thickness Percent Force Draft XG Inches Percent 1.800 r 1. 485 17. 3 3. 76 0. 00327 0, 22 1. 100 25. 9 5.34 0. 00913 0. 83 0. 785 28. G 6. 02 0. 01156 1.47 0. 571 27. 2 6. 01 0. 01155 2. 02 0. 440 23. 0 5. 34 0. 00911 2. 07 0. 351 20. 2 4. 97 0. 00720 2. 20 0. 291 17. 2 4` 64 0. 0064() 2. 20 0. 250 14. 0 4. 37 O. 00550 2. 20

T he drafting was performed in a way to control the crown in a nal product to a value of 2.12 percent. The earlier passes were limited by torque and percent draft. For this reason it is not feasible to .maintain the same amount of crown when the product is thick as compared to the thinner passes. Passes 4 and 5 approach the desired amount of crown, and passes 6, 7 and 8 give the exact percent of crown desired. Since this is a percentage ligure the roll force desired is slightly higher for the thicker passes and the thickness of the plate in the middle as compared to the edges as expressed in inches is greater for the thicker product. This type of drafting practice causes the elongation down the middle of the plate as compared to the elongation down the edge of the workpiece plate to fbe the same particularly on the latter passes where theshape is critical.

FIG. 8 illustrates how the drafting limits control the operation of the rolling mill. The computer considers four different limits in determining the draft to be taken in each given pass. These are inches draft, percent draft, motor torque and separating force. The most important of these as shown in FIG. 8 patricularly on the latter passes is the roll separating force. By properly controlling this force the plate shape can be controlled and mechanical equipment can be protected.

FIG. 9 graphically indicates how the drafting limits are effective relative to cold and hot, either cold or wide workpieces on the one hand or on the other hand, hot or narrow workpieces as compared to thin and thick workpieces. The motor torque limit is more effective for a thick workpiece which is wide and/or cold. The inches draft limit is more effective for a thick piece which is narrow and/0r hot. The roll separating force is more effective for a thin workpiece which is wide and/or cold, and the percent draft limit is more effective for a thin workpiece which is narrow and/ or hot. As is required 6 to control shape, force is the limiting factor on thin wide workpieces.

In FIG. lO there is shown a rolling mill stand, which could be the stand 10 shown in FIG. l, including work rolls 12 and 14 operative with the workpiece strip 32. A left screwdown device and a right screwdown device 102 are operative with the backup rolls to control the roll separating force at respectively the left edge and the right edge of the work rolls. As the workpiece strip 32 leaves the stand 10 a left thickness gauge 104, a center thickness gauge 106 and a right thickness gauge 103 are opertaive with each respective increment `of the workpiece strip 32 to provide thickness signals to the shape' control apparatus 110. In this way the desired workpiece contour or cross-sectional shape can be maintained in accordance with the teachings of the present invention.

It should be here noted that the delivery shape of the workpiece from any given pass or stand of the rolling mill can be monitored visually by a human operator however, thickness gauges lcan be provided to monitor the workpiece shape as illustrated in FIG. l0 of the drawings. A crown control parameter in the operation controlling force equation is provided to correct for undesired errors in the delivery shape which may result from sev eral factors, for example, the temperature build-up at the center of the work rolls as compared to the edges of the work rolls where the water spray and conduction cooling through the bearings and the like are more effective.

As the maximum reduction in accordance with one of the four limits shown in FIG. 9 is determined for a particular schedule, the minimum number of passes is also determined. FIG. 7 illustrates Vsuch a schedule by plotting the thickness versus the passes through the mill stands. lt is required that the initial 1.8 inch workpiece be reduced to 0.25 inch in the minimum number of passes. Point 200 shows the minimum delivery thickness for pass 1 as determined by one of the four limits, point 202 shows the minimum thickness that can be delivered from pass 2, and so forth for points 204, 206, 208, 210, 212 and 214. After pass 8 the workpiece could be 0.24 inch thick which is less than the desired delivery thickness of 0.25 inch. A round olf procedure is used by the computer to modify the schedule so that the delivery thickness after pass 8 will be 0.25 inch, but the drafting pattern will still be approximately the same as the original schedule. The computer chooses new coordinates on the curve to designate the new passes one through Ieight primed, so that the thickness delivered from pass 8 is 0.25 inch. The thicknesses for the other passes are determined by linear interpolation. For instance, the delivery thickness for pass 7 is determined by interpolating between points 210 and 212 to determine point 211 and to retain substantially the same pass reduction as initially provided.

The per unit crown desired in the workpiece after the last pass, PUC, should be maintained in the workpiece on all of the latter passes in order to produce a flat piece which, during the latter critical passes, is 'elongated along the edges the same amount as down the middle of the workpiece. The amount of roll bending required if the roll had no crown would be PUC (H1) where H1 is the entry thickness to the pass. To be more accurate, the delivery thickness from this pass should be used but it is not known at this stage in the calculation. It is usually sufl'lciently accurate to use the entry thickness, if not some iterative process could be used to determine an approximate delivery height and improve on the accuracy by repeating the calculation several times.

If the roll is not cylindrical but hasV some crown, the roll must bend an additional amount, CD. CD is twice the difference in diameter of the rolls at the center as compared to the crown at the edge of the strip being rolled. As an example, for a 100 inch wide material in a inch wide mill having the roll crown shown in FIG. 6, the difference in roll diameter between the center of the roll and 50 inches Vfrom the center is (D10-.006) or 0.004. CD in this case would I'oe equal to 2 .004 or .008.

The upper part of FIG. 6 for a 64 inch work roll shows that the force FC required to bend the roll by the amount of CD is 1.5 million pounds. It therefore follows Vthat the force required on any pass to produce enough roll bending to remove the crown in the roll, CD, and impart enough additional bending to produce a workpiece with a crown of PUC (H1) is F: [PUC(H1) +Centre/CD Two of these cancel to give:

F=[PUC(H1)+CD(CC)] XFC/CD The Ondine control computer 24 shown in FIGURE 1 would include equations for FC and CD as well as this equation for F. Using the example where PUC=.01;

Crown F= (PUC (H1) H1 Required 1.5

PUC (H1) *00mm 0. 25 0.0025 1. 97 0. 50 0. 005 2. 12 1. 0. 010 3. 38 i. 50 0. 015 4. 32 2. 00 o. 020 5. 25 3. 00 0. 030 7. 13 4. 00 o. 04o 9. 00 5. 00 0. 050 10. 9

The above values would be the force limits that would be used at the various pass thicknesses. One of the other limits torque, percent draft, or inches draft may come into play on the thicker passes but this will not harm the shape.

In reference to FIG. 8 the plastic curve 240 is determined from measured data for the particular workpiece material to be rolled. The force required for the desiredV crown is calculated using the above force formula and is shown by the point 242 on the plastic curve to be in the ord-er of 5.6 million pounds. This provides a delivery thickness 244 which is limited by roll separation force. The inches draft limit is calculated by the formula where MD is the maximum inches draft and gives the limit 246. The percent draft limit is calculated by the formula H1D=H1 (1-MPD) where MP'D is the maximum per unit draft and gives the limit 2.48 shown in FIG. 8. The motor torque is calculated by the well known prior art formula HT=f(TH, H1, Tp, Wp, G) and gives the limit 250 shown in FIG. 8. Since the roll separation force is the limit providing the lowest permissible roll force, this is chosen such that the mill spring characteristic curve 252 provides a roll separation in the order of 0.32 inch.

It is therefore seen that the computer control with the proper stored program based on careful study of process requirements in the production equipment ratings and capabilities can utilize the rolling mill to its fullest, and yet assure staying within safe limits. The computer control as'sures good equipment life and minimizes down time caused by wrecking of the rolling mill through excessive 8 overloading.' Since the computer can calculate the number of passes of the workpiece through the mill as well as the drafting practice that is followed, reliable feedback signals of roll force as obtained from the load cells 37 shown in FIG. 1 and mounted within the mill structure are neded in order to take into account the stretching of the mill housing. In addition, the X-ray gauge and width gauge signals are fed from the mill to the computer control for comparison purposes and as a means of upgrading the operation in modifying the information contained in the stored program.

One typical reversing plate mill system receives carbon and alloy steel slabs ranging from 4 inches to 24 inches thick, 40 inches to 75 inches wide and 54 inches to 264 inches in length and weighing up to 70,000 pounds. The mill reduces these slabs by a series of passes through the mill to finished plate ranging in size from g/g inch to inches thick, approximately 200 inches wide, and 125 feet long. This typical plate mill is powered by two 6,000

horsepower, 40/80 r.p.m., 80() volt D C. motors arranged in a twin drive arrangement with each motor being supplied power from a 5,000 kilowatt rectiverter power supply. The slab is brought onto the approach tables to the mill and is passed through the scale breaker, broadsided for a few passes through the reversing mill, and then turned and finish processed for a number of passes through the mill to the iinal plate size desired. Many sensing devices mounted on the processing equipment provide feedback information to the computer control system. These sensing devices include a pulse generating position indicator for the screwdown setting and the side guide positions, hot metal detectorsfor positioning the metal in relation to its stage in process, roll force measuring transducers mounted within the mill housings for indications of forces occurring during rolling which can be translated into stretching etTect-s of the mill housing, X-ray gauges which are used during part of the process to provide feedback information of actual thickness of the metal, and width and length gauges for providing signals to the computer system of the dimensional aspects ofthe workpiece plate and process. In addition, the conventional automatic regulated control systems associated with rolling mills are provided, such as the direct current adjustable voltage drive systems and similar electrical systems including regulating systems, and similar protective features. The computer system governs the overall operation of the rolling mill process, and includes the input information equipment for the computer and central process control along with the necessary input and output devices associated with the command set point control and data transmission features of the system. The input information to the computer can be in punch c-ard form and will include the incoming slab dimensions, the desired plate dimensions and the alloy. Thus the input information required to a system of this type is minimal. The number of passes, the draft for each pass, and the point during therolling operation at which the bars are to 'be turned are all controlled by the computer control.

Since it is important to achieve correct gauge and shape, the most important consideration in the rolling operation is the proper automatic computation and automatic'setting of roll separating force to be used in each pass. Thus the proper draft will be used to cause the right amount of roll force for a given product width and a right amount of roll crown to produce the desired flattened plate. Included in the overall computation made by the computer for establishing the drafting practice, a prediction of the temperature of the plate during each pass in relation to the amount of roll force required i's necessary. The stored program of the computer is arranged such that the number o-f passes and the reduction of the metal in each pass can be changed, once a schedule has been started, if measured force and torque at the rolls is appreciably different from that predicted by the computer. Such a condition is recognized by proper feedback of signals from the senser equipment onthe mill. This will if desired enable the mill to roll each plate in the minimum number of passes thus reducing the time of work in process. The roll force and screwdown settings are used along with the mill constants identifying the modulus elasticity of the mill and other factors to determine the thickness of the workpiece as rolled in accordance with the formula hzS-l-F/M during passes when the workpiece is thicker than two inches. The X-ray gauges are used to measure the thickness of the plate when it is less than two inches. Under such latter conditions the computer compares a calcul-ated thickness using the roll force in comparison with a measured thickness from the X-ray gauge as fed back fromthe gauges. Any errors due to roll wear or changesin temperature of mechanical parts of the mill or other effects are thus taken care of by an automatic correction of the equations being employed in the stored program of the computer.

As parts ofthe mill heat up and cool down and the rolls wear, the slope of the m-ill spring lines remain essentially constant but calibration of the screwdown positioning system must be changed periodically to compensate for resulting dimensional changes in the parts. This is done by monitoring the thickness of the product with X-ray gauges and automatically recalibrating the screwdown positioning system on the last pass in the rolling of each piece.

Thusly, it will be seen that presently available sensing device such as roll separating force transducers, length gauges and hot mill X-ray gauges are very useful tools for monitoring the operation of a rolling mill. An online computer can utilize the information gathered and in this manner control the complicated operation to -produce a quality product at a high rate in spite of variations in incoming workpiece dimensions and temperatures.

It should be understood that the strip shape control teachings of the present invention are intended to be added to or combined with the presently well known rolling mill apparatus. Further it should be understood that the teachings of the present application are readily adaptable to single or multiple stand mills, either tandem or reversible mills. IF-or reversible mills it should be understood that thickness gauges will be provided at the delivery ends of the respective mills for each direction of strip movement.

Although the present invention has .been described with a certain degree of particularity it should be understood that the present disclosure has been made only by way of example and that numerous changes in details of construction and combination and arrangement of parts may be resorted to without departing from the scope and spirit of the present invention.

We claim as our invention:

1. The method of controlling the shape of a workpiece passed through a rolling mill having'a pair of rolls, with t the separation force between said rolls being controlled by a screwdown mechanism, comprising the steps of predicting a pass roll separation force in accordance with a predetermined relationship'with the incoming thickness and width of the workpiece, and the crown of the rolls through use of the force equation wherein PUC is the desired per unit crown, H1 is the 'entry thickness to the pass, CD is proportional to the roll crown, CC is a provided correction factor and FC is the force required to remove the roll crown CD; predicting a pass screwdown position setting in accordance with a predetermined relationship with the desired delivery thickness of the workpiece,said predicted pass roll sep-aration force and a predetermined mill spring characteristic for said rolling mill, and passing the workpiece through said rolling mill between said rolls with said 10 screwdown mechanism positioned in accordance with said predicted pass screwdown position setting.

2. The method of controlling the cross-sectional shape of a workpiece passed through a rolling mill between a pair of rolls, with the separation force between said rolls being controlled by a screwdown mechanism, comprising the steps of predicting a iirst pass roll separation force in accordance with an empirically predetermined relationship with the incoming thickness of the workpiece, the incoming ywidth of the workpiece, and the known crown of the rolls and rthe desired per unit crown of the rolled workpiece; predicting a first pass screwdown position setting in accordance with a predetermined relationship with the desired delivery thickness of the workpiece, said predicted rst pass roll separat-ion force and a predetermined mill spring characteristic for said rolling mill; and passing the workpiece through said rolling mill between said rolls after said screwdown mechanism has been positioned in accordance with said predicted first pass screwdown position setting.

3. The methodof controlling the delivery shape of a workpiece to provide a workpiece thicker in the middle i as compared with the edges after passing a predetermined number of times through a rolling mill having at least one pair of rolls, with the desired delivery thickness of said workpiece after each of said passes being predetermined and with the separation force between said rolls for each pass being controlled by a screwdown mechanism, comprising the steps of predicting for each successive pass the roll separation force in accordance with a predetedmined relationship with the incoming thickness of the workpiece for that pass, the incoming width of the workpiece for that pass, and the crown of the rolls through use of the force equation wherein PUC is the desired per unit crown, H1 is the entry thickness to the pass, CD is proportional to the roll crown, CC is a provided correction' factor and FC is the force required to remove the roll crown CD; predicting a screwdown position setting for each such pass in -accordance with a predetermined relationship with the desired delivery thickness of the workpiece for that pass, said predicted pass roll separation force and a predetermined mill spring characteristic forsaid rolling mill; and successively passing the workpiece through said rolling mill between said rolls with said screwdown mechanism positioned in accordance with said respective predicted pass screwdown position setting for each of said predetermined number of times.

4. The method of con-trolling the shape of a workpiece making at least two passes through a rolling mill having a pair of rolls for each pass with the desired delivery thickness of said workpiece after each of at least said two passes being predetermined, and a screwdown mechanism being provided to control the relative positions of said pair of rolls for each pass, comprising the steps of determining a pass roll 4separation force for each pass in accordance respectively with a first predetermined relationship with at least the incoming thickness of the workpiece for each pass, the incoming width of the workpiece for each pass, the desired per unit crown of the workpiece when delivered from each pass and the crown of the rolls; determining a pass screwdown position setting during the respective pass; sensing the presence of any error in the workpiece actual delivery shape compared to a predetermined workpiece desired shape to provide a correction signal after each pass; and modifying the next pass'roll separation force in accordance with said correction signal provided after a given pass to correct for the shape error present after said given pass.

r'TSQThe method of controlling the delivery shape of a workpiece successively operated upon by shape determining means having at least one crowned roll and including separation controlling means, comprising the steps of deriving a rst operation force in accordance with a predetermined relationship to the crown of said roll wherein this rst operation force is effective to remove lsaid roll crown and to produce a workpiece with a desired per unit crown; deriving a rst operation separation setting for said shape determining means in accordance with a predetermined relationship to the desired rst operation delivery thickness and said iirst operation separation force in accordance with the formula h=S-\F/M,

12 wherein h is the delivery thickness, S is the operation separation setting, F is said operation separation force and M is a predetermined mill spring constant; and operating upon said workpiece with lsaid separation controlling means utilizing said first operation separation setting for said shape determining means.

References Cited by the Examiner UNITED STATES PATENTS 2,726,541 12/1955 Sims 73-885 2,792,730 5/1957 Cozzo 80-562 3,024,679 3/1962 FOX 80--38 3,104,566 9/1963 Schurr et a1. 72-8 RICHARD I. HERBST, Primary Examiner.

CHARLES W. LANHAM, Examiner. 

1. THE METHOD OF CONTROLLING THE SHAPE OF A WORKPIECE PASSED THROUGH A ROLLING MILL HAVING A PAIR OF ROLLS, WITH THE SEPARATION FORCE BETWEEN SAID ROLLS BEING CONTROLLED BY A SCREWDOWN MECHANISM, COMPRISING THE STEPS OF PREDICTING A PASS ROLL SEPARATION FORCE IN ACCORDANCE WITH A PREDETERMINED RELATIONSHIP WITH THE INCOMING THICKNESS AND WIDTH OF THE WORKPIECE, AND THE CROWN OF THE ROLLS THROUGH USE OF THE FORCE EQUATION 